The 115th anniversary of the discovery of X-rays has been commemorated with a
Google Doodle.

The search-engine's logo is shown as an X-ray, with bones forming the letters along with several other items such as keys, coins and a rubber duck.

The Doodle, which is animated to pulse with a radioactive glow around the letters, also contains a nod to Google's "Pigeonrank" April Fool's joke from 2002. The second 'g' in the logo is composed of pigeon feathers and wingbones in a reference to Google's prank announcement that its sophisticated page ranking system was determined by pigeon pecks.

X-Rays - a form of electromagnetic radiation - were first observed in 1895 by Wilhelm Conrad Roentgen, a German scientist who stumbled upon them accidentally when experimenting with cathode rays late at night in his lab.

The fifty-year-old scientist covered a vacuum tube with black cardboard in a darkened room and switched on an electric current. He was astonished to see a greenish yellow glow appear on a cardboard screen that was lying on a chair several feet away.

A week later, he took an X-ray photograph of his wife's hand which clearly showed her wedding ring and her bones.

Roentgen called the rays ‘X’ to indicate they were an unknown type of radiation. He ordered that his lab notes be burned after his death, meaning that much remains unknown about how he made his breakthrough.

X-rays are generated by a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The electrons then collide, creating X-rays.